Of all the hopefuls building flying-car prototypes in garages all over the world, Paul Moller may be the front runner. Moller's Skycar is already a viable machine, drawing on design and technology that's been refined over 40 years of intense effort. He also has the most to lose: The 67-year-old aerospace engineer devoted most of his life, raised and sunk $70 million into the project (in some amazing business ventures), and has two failed marriages to prove his persistence. Fortune tells Moller's story in its December issue.